Pastes which are used in preparing dental impression compositions containing platinum, organopolysiloxanes and fillers are known. These dental impression compositions contain triorganosiloxy terminated diorganopolysiloxanes having SiC-bonded vinyl groups in the terminal units, an organopolysiloxane which contains at least 3 Si-bonded hydrogen atoms per molecule, a platinum catalyst for the addition of the Si-bonded hydrogen to the vinyl groups and a filler as the essential ingredients. These pastes have been added to the other components of the compositions in a weight ratio which range from 1:1 to 7:1. U.S. Pat. No. 4,273,902, to Tomioka et al, discloses in Example 1 forming a paste by mixing a dimethylpolysiloxane having vinyldimethylsiloxy terminal groups with quartz, calcium carbonate and a platinum-siloxane complex and then adding 7 parts of the paste to 1 part of hydrogenmethylpolysiloxane. In Example 2 of the patent, a paste composition containing a hydroxyl-terminated vinylmethylpolysiloxane, quartz, zirconium silicate and chloroplatinic acid is added in a 1:1 ratio to a composition containing a hydroxyl-terminated vinylmethylpolysiloxane, hydrogenmethylpolysiloxane and finely divided quartz.
One advantage of using a paste composition such as described in the present invention is that the amount of platinum catalyst required is substantially reduced while attaining more uniformity in the crosslinking behavior of the composition after storing the paste for a period of time. Also, the use of a small amount of paste in the dental impression compositions avoids testing large quantities of the paste containing platinum, organopolysiloxane and filler. Another advantage of using the paste composition of this invention in dental impression compositions is that the paste composition containing platinum, organopolysiloxane and filler can be rapidly and easily kneaded with the other components of the composition with the bare hands without leaving any trace of the composition on the hands. Still another advantage of the present invention is that the components of the dental impression composition consisting of a diorganopolysiloxane having SiC-bonded vinyl groups, an organohydrogenpolysiloxane containing at least 3 Si-bonded hydrogen atoms per molecule and filler can be stored together.
Therefore, it is an object of the present invention to provide a paste composition which may be combined with the other components of dental impression materials. Another object of the present invention is to provide a paste composition containing a diorganopolysiloxane having SiC-bonded vinyl groups, a platinum catalyst, a hydrocarbon and a hydrophobic filler. Still another object of the present invention is to provide a dental impression composition in which only a small amount of platinum catalyst is required and still achieve uniform cross-linking of the dental impression composition. A further object of the present invention is to provide a dental impression composition in which the diorganopolysiloxane having SiC-bonded vinyl groups, an organohydrogenpolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule and filler can be stored together.